Seiko Case Back Details

[akable]

I was looking through an issue of the Let's Go Suwa No.160 factory magazine from 1969 and saw a short article on deciphering the different case back details.



This should not come of any real surprise to most people here but I though it was nice to see it all listed in one place. It covers the case material, movement and case design numbers, serial number, company crest and case manufacturer.



I did a quick English translation of this as seen below.



While this type of information is common knowledge I decided to do a quick write up on this and to also include some of the more modern information like the case construction codes so it could all be found together.

This summary can be seen here and I please let me know if you spot any obvious errors or omissions. Deciphering Seiko Case Back Information

[Thomas]

Nice Anthony!   


It's cool to see it hand drawn by the original folks.  

And thank you adding the translation and the later documentation at your site.  


That's good to have available "just in case"!!  


- Thomas

[small]

So Seiko wasn't/isn't making thier own cases?

[ajkrik]

Thanks. That's a very informative post. It's nice to have this info for reference purposes.

[akable]

Oct 3, 2017 6:09:40 GMT -8 small said:

So Seiko wasn't/isn't making thier own cases?

Seiko has used multiple suppliers for cases for many years. Some of these are internal, for example the SD and quartz GS model cases are made onsite at the Seiko Epson Shiojiri factory.

Here is an image I took at the factory of some of the dies and jigs for various cases.



and here are some workers performing finishing of the cases.



For other models Seiko manufacture the cases at different locations. These may be a different Japanese factory or one located in China and possibly other countries. The companies that make these could be internal to Seiko or might be a company that Seiko just holds a majority stake in.

One example of these case manufacturers is Hayashi Seiki Seizo Co. Ltd. This is a Japanese company that has a long and extremely close relationship with Seiko. Seiko is the majority owner of the company and they have produced cases for Seiko watches for many years. Here is an example of an advert from 1982 for the company.



As you can see they have been around since 1921 and I am unsure when Seiko purchases a majority stake in them but they work very closely together. Hayashi Seiki Seizo is responsible for many of the high end made in Japan watch cases including many mechanical Grand Seiko models and other fan favourites like the MM300. Hayashi Seiki Seizo also produce watch cases for other brands as well including the Casio Oceanus models.

The sales office used to be located in the main Seikosha Kameido location till it closed in 2002. At this time the Tokyo sales office located to Sumida-ku. SII Press Release - Office Relocation

After the 2011 tsunami in Fukushima the Hayashi Seiki Seizo facility was almost completely destroyed and they moved their operations temporarily to a Seiko factory to continue production.

The company has a SII sign in their factory car park so they do not really attempt to hide their connection to SII.

[small]

Do we know what the case code are? I have seen Several different on my watches, without looking beyond my wrist I see TL and I know I have seen P inside a box maybe? I wonder if there isn't a key? 

[akable]

The Seiko case servicing guide lists the different case construction codes. A P in a box on the back indicates that the crystal is glued into the case and should be pressed out after placing the case or bezel with the glass into boiling water for a few minutes to soften the glue. The replacement crystal is then glued into position using Seiko S-310 glue.